DYNAMICAL CHIRAL-SYMMETRY BREAKING FROM VARIATIONALLY IMPROVED PERTURBATIVE EXPANSION

We review how a specific resummation of the so-called ''delta-expansio n'', applied to the QCD Lagrangian, transforms the ordinary perturbati ve expansion in alpha(s) into an expansion in an arbitrary mass parame ter, around the basic scale <(Lambda)over bar>. When applied to the po le mass, the resulting expression may be interpreted as a dynamical ma ss ansatz, to be optimized with respect to the new expansion (mass) pa rameter. The construction is generalized to obtain estimates of the or der parameters of the SU(n(f))(L) x SU(n(f))(R) (n(f) = 2, 3) symmetry breakdown.